1. Field of the Invention
The present invention relates to a desensitization printing process, more particularly, to a desensitization printing process which comprises using in combination a printing plate consisting of hydrophilic image areas and oleophilic non-image areas and a desensitizer specified by its specific contact angle with the non-image areas.
2. Description of the Prior Art
It has long been known to obtain color images through a contact reaction between an electron donating or proton accepting colorless organic compound (hereinafter referred to as a color former) and an electron accepting or proton donating solid acid (hereinafter referred to as a color developer). As a specific use of this phenomenon, there can be illustrated pressure-sensitive copying papers (see, e.g., U.S. Pat. Nos. 2,505,470, 2,505,489, 2,550,471, 2,548,366, 2,712,507, 2,730,456, 2,730,457, 3,418,250, 3,672,935, etc.), heat-sensitive recording papers (see, e.g., Japanese Patent Publications 4,160/68, 7,600/68 and 14,039/70 and U.S. Pat. No. 2,939,009), and the like. Furthermore, there is known a printing process for obtaining colored images by supplying a color former-containing ink to a color developer-coated sheet (see German Pat. No. 1,939,962).
Since these recording sheets comprise a support having coated on the whole surface thereof a color developer layer, it is common to desensitize areas of the color developer layer where recording is not desired by coating on the areas a desensitizer-containing printing ink via typographic printing or intaglio printing. As the desensitizer, organic amines or the quaternary salts thereof (see U.S. Pat. No. 2,777,780), tertiary amines wherein monoalkylamine, aralkylamine or ethanolamine is chemically combined with ethylene oxide (see Japanese Patent Publication 35,697/71), spiroacetal diamines and a reaction product between spiroacetal diamine and an oxirane group-containing compound (see German Patent Application OLS 2,343,800), N-(aminoalkyl)-lactams or derivatives thereof (see German Patent Application OLS 2,359,079), amidines as shown in German Patent Application OLS 2,361,856, amines as shown in Japanese Patent Application 132,331/73, silane compounds as shown in Japanese Patent Application 32,337/74, and the like have been used.
However, all desensitizers described above are water-soluble and hydrophilic.
Generally, printing processes can be classified as a: (1) typographic printing process, (2) intaglio printing process, (3) lithographic printing process, (4) stencil printing process, etc.
Each of these printing processes naturally requires a printing ink suitable therefor.
Typographic printing processes and intaglio printing processes have heretofore been employed as desensitization printing processes. However, the very popular lithographic printing process has not been so employed, since it has been technically impossible to prepare a desensitizing ink having suitable properties for lithographic printing.
Lithographic printing involves forming images using a printing plate consisting of hydrophilic non-image areas and oleophilic image areas, first adhering water (hereinafter referred to as damping water) to the hydrophilic areas of the printing plate, then adhering an oily printing ink to the image-forming oleophilic areas and transferring the ink directly or indirectly onto the materials to be printed.
in this case, damping water adhering to the hydrophilic areas repels the oily printing ink, and hence the printing ink adheres only to the image-forming oleophilic areas, and is then printed to form images. Therefore, when a printing ink contacting an hydrophilic desensitizer which is not damping water-repellent is used, such a printing ink becomes mixed with the damping water adhering to non-image areas of the printing plate, and images cannot be formed by lithographic printing.
Since lithographic printing has the advantages that plate-making can be effected rapidly and inexpensively and that printed images are of good quality and uniform, it has currently become the most typical printing process, and lithographic presses have come into wide use.
However, it has heretofore been impossible to conduct desensitization printing by lithographic printing. Thus, the art has strongly desired a desensitization printing process which can be effected using a lithographic press.
The present invention provides the art with such a process.